Photoelectric precision camera range finder with optical verification



United States Patent l1ll3,529,528

PHOTOELECTRIC PRECISION CAMERA RANGE FINDER WITH OPTICAL VERIFICATION 6Claims, 4 Drawing Figs.

U.S. Cl 95/44, 350/46, 355/55, 356/4 Int. Cl G03b 3/00 Field ol Search95/44, 44C,

Pri/nary Examiner-.lohn M. Horan Assistanr Examiner--Richard L. Moses Attorneys- Krafft and Wells ABSTRACT: A range nder device fior camerascomprising an optical range finder for coarse visual control of thecamera range setting as well as a photoelectric range flnder for aprecise reading of the range setting, the optimal setting beingindicated when both readings simultaneously indicate their optimalvalueA The optical range finder is either ofthe triangulation type,split image type, oriof the ground glass type, while the photoelectricrange finder uses two photo-resistors in a differential balance typecircuit supplied by an AC-current. The arrangement is suitable foradaptation to range finder" cameras as well as to single lens reflexcameras.

Pdtented Sept. 2v2, 1970 Sheet l of 2 ai 9i /24 /NVENTOR Ludwig Leitz Wbp Zdi ATTURNEYS 20a /Qa /9 20 Patented Sept. 22, 1970 Sheet L of 2/NVENTOR Ludwig Leiz W ZUM -ATTORNEYS PHOTOELECTRIC PRECISION CAMERARANGE FINDER WITH OPTICAL VERIFICATION CROSS-REFERENC E TO RELATEDAPPLICATIONS Reference is made to applicant's co-pending applicationSer. No. 686,569, filed Nov. 29, 1967, now U.S. Pat. No. 3,529,527.

BACKGROUND OF THE INVENTION l. Field of the Invention The presentinvention relates to range finding devices in photographic cameras, andmore particularly to photoelectric range finding devices.

2. Description of the Prior Art lt is well known to those skilled inthis particular art to guide the two light beams of, for example, acoincidence-type range finder to two photoelectric receivers. Thesereceivers consist each of an arrangement of elongated photosensitiveelements on which the light beams are simultaneously incident. Anelectric circuitry is provided for comparing the voltage difference ofthe signals generated in the elements by said two light beams, whichmeans comprise a measuring instrument having an indicating needle. Rangefinding is accomplished by adjusting the optical elements of the rangefinder until the deflection of the needle of the measuring instrument isa minimum.

However, it was found that minimum needle deflection may result, eventhough the range finder has not yet been adjusted to the correctdistance. Such erroneous adjustments occur primarily when the objectswhose distance is measured are surrounded by an object space of periodicstructure containing a plurality of similar objects locatedside-by-side, such as, for example, a row of trees or of uniformedpersons. From such periodic structure equal light fluxes can originatewhich may not come from the object itself but from other object spaceportions, from which by sheer coincidence a light flux may emerge whichequals in intensity the light flux impinging on the photoelectricreceivers from the object. This, however, may not be noticed by theoperator.

It is therefore an object of the present invention to provide a rangefinder device where the degree of adjustment is indicated as aphotoelectric precision reading as well as in an optical range findingimage, so as to avoid erroneous adjustments.

This object is attained by combining in a photographic camera aphotoelectric precision range finder and an optical range finder. Thelatter then serves as a coarse adjustment indicator, while thephotoelectric reading is used only for the fine adjustment readingwithin a range where the abovedescribed problems of spatial periodicityis no longer present. During the initial adjustment, the object itselfis observed through a split-image-type, or coincidence-type, orgroundglass-type optical range finder. The subsequent corrective fineadjustment is made while observing the reading of the photoelectricrange finder, which may be shown by a moving instrument needle. Thebasic idea of the new device is to permit a coarse lens settingsufficiently close to the correct position by means of the optical rangefinder so that the axes of the two range finder beams are alreadygenerally directed to the object to be measured, consequentlyeliminating the danger of one of the photoelectric receivers beingexposed to light rays of object intensity, which actually do not resultfrom the object.

DESCRIPTION OF THE DRAWINGS The invention will be more fullycomprehended from the following description when taken in conjunctionwith the accompanying drawings wherein FIG. 1 is a perspective sectionalview of a range finder camera in which an optical and a photoelectricrange finding device are incorporated,

F IG. 2 shows schematically a wiring diagram of the photoelectric rangefinder,

` of the invention;

FIG. 3a isa partial rear view of the penta prismvand the photoelectricreceivers of the embodiment of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I thecamera l is provided with an optical range finder of known design. Thisrange finder comprises two objective lenses 2 and 3 and one ocular 4.Objective lens 2 and ocular 4 form at the same time the view finder ofthe camera.

In the path of the view finder light beam between objective lens 2 andocular 4 there is disposed a semi-transparent mirror 6 at an angle of 45to the optical axiis. By said mirror the second range finder light beamimpinging from objective lens 3 via a mirror 5 is reflected into theocular 4. Mirror 5 is mounted on a pivotable shaft 5a which is in rigidconnection with a lever 5b. A spring 7 exerts a force on lever 5bthereby keeping the free end portion of lever 5b in operative connectionwith a cam 8. The latter is part of the camera objective lens 70 and isrotatable with said lens for distance adjustment purposes.

The above described elements by themselves constitute a known opticalrange finder of the split-image type or coincidence-type.

The camera 1 is further provided with two semi-transparent mirrors 10,11 which are arranged, one in the path of each range finder light beam.By said mirrors l0, 1l a portion of each beam is reflected to separatephotoelectric resistors l2, 13

through field lenses 12a, 13a. The photoelectric resistors are elementsin a Wheatstone bridge circuit, as shown in FIG. 2, which furthercomprises the ohmic resistors 14, 15, further ohmic resistors 16, 17,18, 19, 20 and current rectifiers 16a, 17a, 18a, 19a, 20a.

The photoelectric resistors are of identical design, shape andelectrical properties. Each one consists of signal electrodes 21, 22,23, 24, 25 and 31, 32, 33, 34, 35 respectively which are electricallyseparated from each other and are arranged in parallel. One commonelectrode 29 and 39 respectively is provided in each photoelectricresistor. The signal electrodes 21 through 25 and 31 through 35 areconnected in pairs and each pair is connected to a :series arrangementof one current rectifier 16a through 20a and one ohmic resistor, theohmic resistors being connected in parallel to terminal D in thecircuit.

The Wheatstone bridge is supplied with an AC current at the,terminals A,B and the measuring instrument 60 is connected between the terminals Dand C. The field lenses 12a, 13a are arranged in front of thephotoelectric resistors.

The above described elements constitute a photoelectric range finderwhich functions in the following manner: If, on the photoelectricresistor 12, light beams are incident from the details of a certainobject to be measured, the different photosensitive elements between thesignal electrodes 2l through 25 will assume different resistance valuesaccording to the intensities of said light beams originating from saidobject details. Equal resistance values will be assumed by thephotosensitive elements of resistor 13 if thepivotable mirror 5 in frontof the resistor 13 is adjusted to a position wherein it reflects on theresistor 13 light beams emitting from the same object details as thelight beams which are incident on the resistor l2. Under this conditionof adjustment the` bridge is balanced. At the terminals "u" through ehalf of the supply voltage can be measured. lf, however, the objectdetails imaged on both photoelectric resistors l2, 13 do not coincide,the voltage of at least one of the terminals a through e will bedifferent from the half supply voltage. The current flowing through thisterminal causes the needle of the measuring instrument 60 to bedeflected. As is well known to those skilled in the art, range findingwith photoelectric range finders is accomplished by directing the one ofthe photoelectric resistors in front of which the optical elements arerigidly arranged to the object to be measured. Then the pivotableoptical elements in front of the second photoelectric resistor arepivoted until the needle deflection in the measuring instrument is aminimum. The position of' the pivotable optical elements can be readagainst a scale which may be calibrated in distance units, e.g. in feetor meters.

The novel range finding device according to the invention is voperatedin two steps, by first adjusting the camera objective lens 70 bymanually rotating said lens while viewing the image of the opticalcoincidence-type or split image-type range finder through ocular 4.After the objective lens 70 has thus been set coarsely to the objectdistance, the second step, which is the corrective fine adjustment ofthe objective lens to the object distance, is performed also by manuallyrotating lens 70, however, this time while observing the deflection ofthe needle of instrument 60, for example, through an auxiliary ocular4a.

Emphasis is put on the fact that the novel range -finding device is byno means limited to those cameras which in the art usually are termed"range finder" cameras. The new device can equally advantageously beemployed with so-called single lens reflex cameras, if said cameras areadditionally provided with a photoelectric range finding device asdescribed above.

Particularly satisfactory results are obtained if the photoelectricresistors l2 and 13 are disposed in the place where in applicantsco-pending application Ser. No. 686,569, filed Nov. 29, 1967, thedeviating wedges are located. FIGS. 3 and 3a show the resistors l2 and13 arranged to the rear side of the camera and beneath the enteringsurface of penta prism 80. ln this place the resistors are particularlyadapted to be illuminated by light beams from large aperture imageportions of the objective lens 8l, after reflection of said beams fromthe silvered and inclined rear surface portions y80a and 80b of thepenta prism 80. The photoelectric range finder incorporated in thesingle lens reflex camera makes thus use of a considerably enlarged baseline in substantially the same manner as the optical coincidence-type orsplit image-type range finder which is disclosed in my abovementionedco-pending application.

Below the main ocular 82 the camera has a second ocular 84 through whichthe photoelectric indicator 60 can be observed. The electric circuitryis the same for both embodiments shown.

Range finding with a single lens camera as illustrated in and describedwith reference to the FIGS. 3 and 3a is accomplished in much the sameway as is done with range finder cameras, It involves an initial coarseadjustment of the lens 81 to the object distance while viewing anintermediate image of the object through the ocular 82 on the viewingscreen or ground glass 83, followed by a corrective fine adjustment byobserving the needle deflection in the instrument 60 through ocular 84.

Instead of being provided with the resistors 12, 13 the reflex cameramay of course have a conventional central split image range findercomprising two deviating wedges in the central ground glass or viewingscreen portion. The two bundles of light emerging from the wedges may bedivided into two portions each, with one portion of each bundle beingreflected'to the ocular and the other portions being conducted to thephotoelectric receivers. The light rays emerging from the deviatingwedges are thus used both for coarse and for fine adjustment.

l claim:

l. ln combination with a photographic camera having a housing, a rangefinder device comprising:

optical range finder means mounted in said camera and responsive tofirst and second light fluxes originatingfrom object areas having anindication of the camera range setting;

photoelectric range finder means mounted in said camera including afirst light flux sensing element located in the path of said first lightflux and a second light flux sensing element located in the path of saidsecond light flux, said two light flux sensing elements connected toindicator means responsive to differential changes between the two lightfluxes, thereby discriminating between the condition when the lightfluxes originate from unequal object areas and the condition when thelight fluxes received are identical in that they originate from a commonobject area or from separate light flux equivalent object areas; and

means in said housing for simultaneous viewing of said indication of thecamera range setting and said indicator means whereby furtherdiscrimination is obtained between the condition when the `identicallight fluxes originate from a common object area and the condition whenthey originate from separate, light flux equivalent object areas wherebythe optical range finder means gives a coarse visual control of thecamera range setting and v the photoelectric range finder means givesthe precise reading of the camera range setting.

2. The device as defined in claim 1, wherein the photoelectric rangefinder means further includes a power source supplying alternatingcurrent to its circuitry which is of the differential-balance-type, twoidentical photo-resistors in this circuitry serving as thelight-flux-sensing elements, and optical means directingthe light fluxoriginating from at least a portion of the object area to saidresistors, whereby the portion of the object area received by at leastone of the resistors shifts in response to changes in the camera rangesetting.

3. The device as defined in claim 2, wherein the optical range findermeans are of the triangulation-type and include two spaced imagereceiving means for viewing of at least a portion of the object areathrough each of said means, and mirror means to combine the two imagesthus received into a coincidence-type comparison image, the mirror meansinclud'- ing orientable means for the shifting of at least one of theobject area portions viewed in response to changes in the camera rangesetting; and wherein the photoelectric range finder means furtherinclude optical means in the path of each of the two images received bythe optical range finder means, thereby deflecting a fraction of thelight flux from the two images to the two photo-resistors forsimultaneous optical andl photoelectric comparison of the two imagesreceived.

image-receiving means also serves as a view finder means and includes aview finder/optical range finder ocular, the coincidence-type comparisonimage being a part of the view finder image; and wherein thephotoelectric range finder means further includes as in-Y dicator meansa movable needle, and further includes a second ocular located adjacentto the view finder ocular for visual reading of the needle position. 5.The device as defined in claim 2, wherein the optical range finder meansinclude, in combination with a single lens reflex camera, a movablemirror, a horizontal imaging screen for the reception of an intermediateimage, a field lens above the screen, a pentaprism thereabove, and anocular serving both as a view finder ocular and optical range finderocular; and wherein the photoelectric range finder means include mirrormeans located on the back side of the pentaprism ahead of the ocular andlaterally outside the image field; the two photo-resistors being locatedbetween the field lens and the pentaprism outside the image field andarranged sideby-side in the form of parallel, elongated parts tilted inopposite directions around a common transverse surface line, wherein thelast-mentioned mirror means reflect a portion of the intermediate imagefrom the screen onto the photo-resistors, whi'ch latter registeridentical light fluxes when the intermediate image is in focus anddifferent light fluxes when it is out of focus.

3 ,5 2 9 5 2 8 5 6 6. The device as defined in claim 5, wherein theoptical the photoelectric range finder means further includes as inrangefinder means are of the ground-glass-type, the interdicator means amovable needle, and further includes an mediate image created 0n theimaging screen being visible in ocular located adjacent to the viewfinder ocular for the view finder/optical range finder ocular; andwherein visual reading of the needle position.

